Reducing metal uptake in vegetables irrigated with stormwater
While biofilters are a stormwater treatment technology there is also the potential to use them for urban agriculture, given that they are vegetated systems. However, it has been found that vegetables irrigated with stormwater can contain concentrations of cadmium (Cd) and lead (Pb) that exceed the guidelines set by the World Health Organization (WHO). The aim of this study was to investigate the effectiveness of various filter media amendments for reducing the uptake of Cd and Pb into the edible portions of vegetables. Three types of amendments – zeolite, hydroxyapatite and lime – and three different vegetable types – broad bean (Vicia faba), kale (Brassica oleracea Acephala Group) and radish (Raphanus sativus) – were tested in laboratory-scale biofilter columns. This study found that metal concentrations in the edible portions of plants were below the WHO and Food Standards for Australia and New Zealand guideline values except for Pb in radish. The effectiveness of the amendments was dependent on the metal. Hydroxyapatite was found to be most effective for restricting plant uptake of Pb while Cd uptake was most effectively restricted by lime. Vegetable type was also found to influence plant metal uptake. Radishes were found to have the highest Pb and Cd concentration in the edible portion compared to kale or broad bean pods. This is most likely due to the edible part of radishes (i.e. the root) being in direct contact with the upper portion of the filter media, where metals predominantly accumulate, and suggests that root vegetables may not be suitable for cultivation in stormwater biofilters.